Interferometric evaluation of the sensitivity of accelerometers to differential heating

Laser interferometry is the preferred method currently used by National Metrology Institutes for primary calibration of accelerometers. Highly accurate calibrations require well controlled environmental conditions. Laboratories usually focus on the control of ambient air temperature and humidity. Another important Source of influence is the vibration exciter, which besides uniaxial motion can generate undesirable secondary effects. This paper will treat the problem of differential heating of an accelerometer under calibration, when Caused by a rise in temperature of the vibrator moving element. A simple device used to evaluate the change in the charge sensitivity of an accelerometer due to heating through its mounting base is presented. The sensitivity to differential heating can then be determined by the use of accurate interferometric methods. The knowledge of this sensitivity enables the calibration laboratory to correct the calibration results obtained with vibration exciters, which exhibit significant temperature variations. For instance, some commercial models can present variations higher than 20 degrees C, when the Bessel function J1 minimum-point method is applied. The experimental setup, which has been developed at INMETRO to evaluate this characteristic is described and some measurement results are presented.